Gage control method including consideration of plate width effect on roll opening

ABSTRACT

A PLATE MILL GAGE CONTROL METHOD IS DESCRIDED WHEREIN THE ROLL OPENING AT THE MILL CENTER LINE (AS DETERMINED IN CONVENTIONAL FAHSION FROM THE DESIRED DELIVERY GAGE, THE PREDICTED MILL STRETCH AND ANY CHANGES IN THE CENTER LINE DIAMETER OF THE MILL ROLLS FROM THE LAST MILL CALIBRATION) IS MODIFIED BY AN AMOUNT SUBSTANTIALLY EQUAL TO THE TOTAL SPACE EXISTING BETWEEN ADJACENT ROLL SURFACES IN AN UNLOADED CONDITION AT A POINT CORRESPONDING TO THE EDGE OF THE PLATE TO BE ROLLED. THIS MODIFIED ROLL OPENING THEN IS EMPLOYED TO POSITION THE ROLLS FOR REDUCTION OF PLATE GAGE.

D 9 D. J. FAPIANO 3,625,036

GAGE CONTROL METHOD INCLUDING CONSIDERATION OF PLATE WIDTH EFFECT ON ROLL OPENING Filed April 28, 1969 2 sheets-sheet 1 ISCREWDOWN DRlVE 28 9 srmr-wencooea 130 LOAD ceu.

32 I4 5 \8 i l' COMPUTER PLATE WIDTH u WIDTHS d 8 ID 42 NJ (I U 5 u! U a: 0 LL i INCREASE-- STRETCH INVENTOR.

v DONALD J. FAPIANO HIS ATTORNEY Dec. 7, 1971 D. J. FAPIANO 3,625,036

GAGE CONTROL METHOD INCLUDING CONSIDERATION OF PLATE WIDTH EFFECT ON ROLL OPENING Filed April 28, 1969 2 Sheets-Sheet 2 j 4 sa 1 f ic 44 United States Patent 3,625,036 GAGE CONTROL METHOD INCLUDING CON- SIDERATION F PLATE WIDTH EFFECT ON ROLL OPENING Donald J. Fapiano, Scotia, N.Y., assignor to General Electric Company Filed Apr. 28, 1969, Ser. No. 819,723 Int. Cl. B211) 37/00 US. Cl. 72-6 6 Claims ABSTRACT OF THE DISCLOSURE A plate mill gage control method is described wherein the roll opening at the mill center line (as determined in conventional fashion from the desired delivery gage, the predicted mill stretch and any changes in the center line diameter of the mill rolls from the last mill calibration) is modified by an amount substantially equal to the total space existing between adjacent roll surfaces in an unloaded condition at a point corresponding to the edge of the plate to be rolled. This modified roll opening then is employed to position the rolls for reduction of plate gage.

BACKGROUND OF THE INVENTION The present invention relates generally to metal deforming and more particularly to a gage control method for use in rolling metal plates.

conventionally, metal plates are defined as flat rolled products which have an edge gage of 0.230 inch or thicker when 8 inches or more in width and 0.180 inch or thicker when more than 48 inches wide. Plates, used for bridges, buildings, ships, storage tanks, and many other applications, are rolled from thicker slabs or slab ingots. Rolling operations are performed either in reversing mills, in which the plate passes back and forth through the same set of rolls, or in continuous mills, in which the plate passes in succession through several sets of rolls arranged in tandem. In either type of mill, the passage of a plate between a set of mill rolls during a rolling operation gives rise to roll separating forces which distort or stretch the mill. As a result, the delivery gage or gage following the rolling operation is greater than the gage or distance by which the mill rolls were initially separated. The initial separation of the mill rolls is referred to as the unloaded roll opening.

In determining the unloaded roll opening needed to produce a desired delivery gage during a rolling operation, it is standard practice to use mill stretch data which indicates the amount of stretch for dilferent levels of roll separating forces for plates of particular compositions, widths, and temperatures. The derivation of stretch data and the prediction of roll separating forces may be carried out by known techniques. As the particular techniques used are not important, they are not discussed here.

The position of the mill rolls is normally monitored by a position sensing device which actually senses the angular positions of roll-adjusting screws that bear against end supports for one of the mill rolls. A commonly used position sensing device is a shaft position-to-digital converter or encoder consisting of a disk having binary-coded contact strips which may be read by means of parallel output brushes to produce a digital count representative of the screw position and thus the mill roll position.

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To calibrate or zero the mill, as is normally done at the beginning of a work shift, the rolls are forced together or loaded by the roll-adjusting screws until a predetermined force level is sensed by a force transducer located between one of the screws and one of the roll supports. The shaft encoder count is noted. The stretch of the mill is also determined from a special facing stretch curve and the shaft encoder count for this magnitude of stretch is established. The shaft encoder count when the rolls first touch or are zeroed is derived by adding the stretch count to the count observed at the calibrating load level. Because the rolls normally have a positive crown (center line diameter greater than end diameter), the zeroed rolls touch at the center line only.

To illustrate the calibrating process using arbitrarily selected numbers, assume that the shaft encoder count increases by one count for each mil (.001 inch) of roll movement as the rolls move away from one another. If, at the predetermined force level, the shaft encoder count is zero and the stretch is known to be 50 mils, the shaft encoder count for zeroed rolls is 50.

Because the shaft encoder actually senses screw position and not roll face position, changes in roll diameter occurring between calibrations due to thermal expansion or wear are accompanied by changes in the shaft encoder reading for zeroed rolls. For example, if the center line diameters of the rolls have increased 30 mils above the original diameters due to thermal expansion since the last time the mill was calibrated, the rolls must be moved 30 mils further apart to zero them, and the zeroed rolls count must be changed to 50 plus 30 or 80. Similarly, if the rolls have worn to 20 mils less than the original center line diameter, the rolls must be closed 20 mils and the zero shaft encoder count changed to 50 minus 20 or 30. Changes in center line roll diameters may be determined by actual measurement of the rolls or may be predicted from measurements of rolled plates, temperatures, and the amount of time the rolls have been in use.

According to the prior art, the center line unloaded roll opening for a rolling operation is established as follows. Assume, for purposes of illustration,

(1) That the shaft encoder count for zeroed rolls is 50,

(2) That the desired delivery gage is 500 mils, and

(3) That the mill stretch for the predicted roll separating forces is 200 mils.

The shaft encoder count for the proper center line (according to the prior art) unloaded roll opening would be 50 plus 500 minus 200 or 350. The position of the mill rolls is then adjusted until the actual shaft encoder reading equals the calculated reading.

The prior art technique of calculating roll position assumes that it is permissible to use the center line of the rolls as the reference for establishing an unloaded roll opening based on plate edge gage and mill stretch at the plate edges. This assumption is permissible only where plate width does not change greatly from piece to piece, or where a reliable and accurate feedback of plate edge gage is available prior to the last rolling operation in a series of operations performed on the plate. Where width changes are small, roll opening adjustments based on measurements of the final gage of previously rolled plates will gradually eliminate the zeroing error in any form of closed loop gage control system. Where an automatic gaging device is available, some correction is possible even on the first plate in a series of uniformly-wide plates.

By observing the actual gage following each operation and comparing it to the predicted gage, appropriate corrections may be made prior to the last rolling operation to eliminate observed gage errors.

However, the prior art technique results in undesirably heavy reliance on the accuracy of the gaging device, particularly where widths change abruptly from plate to plate.

SUMMARY OF THE INVENTION The present invention is an improvement in gage control which recognizes that the configuration of the rolls and the width of the plate being rolled must be taken into consideration in the first instance to avoid undue reliance on gaging devices. A base figure is established for each unloaded roll opening as a function of the desired delivery gage, the predicted mill stretch, and the changes in center line diameters of the mill rolls since the last time the mill was calibrated. An offset is determined as a function of the effective crown on the mill rolls, the length of the mill rolls, and the width of the plate to be rolled. The mill rolls are positioned according to the combination of the base figure and the offset before a rolling operation is performed.

DESCRIPTION OF THE DRAWINGS While the specification concludes with claims particulaly pointing out and distinctly claiming that which is regarded as the persent invention, details of the invention may be more readily ascertained from the following detailed description when read in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of a rolling mill control system showing only those elements needed to practice the present invention;

FIG. 2 is a graph of a family of mill stretch curves for plates of different widths;

FIG. 3 is an exaggerated front view of a pair of mill rolls in a two-high mill; and

FIG. 4 is an exaggerated front view of a set of mill rolls in a four-high mill.

DETAILED DESCRIPTION Referring now to FIG. 1, a plate mill consisting of a pair of opposed rolls and 12, each backed by one of a pair of larger rolls 14 and 16, is shown during a rolling operation being performed on a plate 18 passing from left to right through the mill. In this type of mill, commonly known as a four-high mill, the opposed rolls 10 and 12 are designated work rolls whereas the larger rolls 14 and 16 are designated backup rolls. The relative positions of the work rolls 10 and 12 are controlled by a screwdown drive including a screw 20 extending through a threaded bore in a top plate 22 in a mill housing, of which only top plate 22 and a base plate 24 is shown. The vertical position of the screw 20 with reference to the top plate 22 is controlled by a screwdown drive 26 and is monitored by a shaft encoder 2-8. The lower end of the screw 20 bears indirectly on one end support for the backup roll 14 through an interposed force transducer, such as load cell 30, which measures the forces tending to separate the work rolls 10 and 12 as the plate 18 undergoes reduction. While a single screw 20 is shown, it shoulld be understood that the screwdown drive also includes a second screw seated against the end support at the opposite end of backup roll 14. When the position of roll 14 and thus the position of work roll 10 is to be adjusted, both screws are rotated synchronously by one or more drive motors in screwdown drive 26.

The edge gage of the plate 18 delivered from the mill is monitored by a thickness gage which may be an X-ray gage or any other suitable type of gage. Assuming that the thickness gage is an X-ray gage, the gage includes a radiation source 32 located above one edge of the plate 18 and a detector 34 located below the same edge in line with the output of the source 32, Signals representing measurements made by the thickness gage are applied to a computer 36 which also receives inputs from the shaft encoder 28 and the load cell 30. An additional input to computer 36 is representative to plate width. The plate width may be determined by any suitable width gage of one is available. Where there is no available width gage, the width should be known with sufficient accuracy from the processing instructions which include target dimensions.

As the plate 18 passes between the work rolls 10 and 12, it tends to force the rolls apart by distorting the rolls, the roll supports, and the mill housing. The amount of roll separation or stretch at the edges of a plate of a given width is a function of the roll separating force, the composition, and the temperature of the plate. When plotted as a function of force, a mill stretch curve is shown to be non-linear. FIG. 2 shows three mill stretch curves for plates of widths A, B, and C. In determining the stretch of the mill at the edges of a plate of given width, such as width A, the intercept of a line representing the predicted roll separating force F1 and the appropriate stretch curve (for width A) is located. The location of this intercept on the stretch curve defines a stretch S1 which indicates the amount by which the roll separation increases at the edges of the plate during the rolling operation.

The edge gage of the rolled plate has been considered, according to the prior art, to be equal to the sum of the unloaded roll opening established as described at the mill center line and the stretch S1.

The present invention recognizes that the roll gap configuration and the plate width must also be taken into account in initially establishing a center line unloaded roll opening needed to produce a plate having a particular desired edge gage. Referring to FIG. 3, representing a pair of zeroed rolls in a two-high mill, it is seen that the total roll gap at the ends of the rolls initially equals one crown (C) with each roll contributing one half of the total. The roll gap at a distance /2W from the center line of the rolls is less, being a function of the shape of the rolls themselves. Since the rolls are generally parabolic, the roll gap at distance /2W is equal to the roll gap at the ends of the rolls minus the roll gap at the center line times the square of the ratio of the distance /2W to the distance /2L from the center line to the ends of the rolls. More succinctly,

where G is the roll gap at the distance /2W, G is the roll gap at the ends of the rolls, G is the roll gap at the center line of the rolls, W is the plate width, and L is the roll length. For the zeroed two-high mill illustrated in FIG. 3, the term G LOC.

In a four-high mill, the term G -G is initially equal to twice the crown on one of the work rolls. Referring to FIG. 4 for an explanation, the maximum gap between work rolls 38 and 40 is equal to 1.0C just as in the twohigh mill described in connection with FIG. 3. In addition, roll gaps equal to /2C exist between the work rolls 38 and 40 and their respective backup rolls 42 and 44. These additional gaps add one full crown to the effective crown, yielding a total effective crown of 2.0C. Since backup rolls normally have zero crown, there is no contribution to total crown from them. However, where backup rolls do have a ground crown, the two backup rolls do contribute 1.0 backup roll crown to the total effective crown.

The discussion has dealt only with the initial effective crowns in both two-high and four-high mills. It should be understood that the effective crown does not remain at a fixed value during rolling, but tends to increase due to uneven thermal expansion across the face of the mill rolls and tends to decrease due to uneven wear across the face of the mill rolls. In practicing the invention, the most current effective crown value is used. Current effective roll crown values may be estimated by a mill operator on the basis of the condition of plates being rolled.

As an alternative method of obtaining current roll crown values, the relationship between roll separating forces, measured plate crowns, and roll crowns may be used. Generally, the roll separating force F needed to form a plate crown P C may be calculated with an equation having the form:

where k k and k are constants fixed by the properties of the mill and plate whereas RC represents the effective roll crown. Rearranging this equation 1 r RC=E( r21 0) plate width 2 G 2 X crown length For a one hundred inch wide plate being rolled by 150" work rolls having an effective crown of 15 mils, the offset is or approximately 13 mils, meaning that a center line shaft encoder count of 350 is equivalent to a shaft encoder count of 363 at the edges of a one hundred inch plate.

Since it is the count for the roll opening at the edges of the 100 inch plate which must equal 350 in order to produce a plate having an edge gage of 500 mils, the count at the center line must be reduced from 350 to (350-13) or to 337.

To simplify computation of the offset, a linear equation may be used to calculate approximate offsets based on a linear roll gap. This equation would have the form where G is the approximate offset, k is a constant determined by the configuration of the mill rolls, C is the effective crown depending on the type of mill, W is the width of the plate being rolled, M is the minimum width to be rolled, and R is the length of the mill rolls. For parabolic rolls, the constant k would have a value between 1.5 and 2.0.

It is to be understood that the base figure and the offset are calculated prior to each rolling operation in a schedule regardless of whether the schedule is carried out in several passes through a reversing mill or in a single pass through a plurality of stands in a continuous mill. Calculating the offset in the first instance, reduces reliance on an automatic gaging device to provide after the fact measurements of errors caused by disregard of roll gap configuration and plate Width.

What is claimed is:

1. For use in each rolling operation in a plate rolling mill, a gage control method including the steps of:

(a) establishing a base figure for the roll opening at the mill center line in accordance with the desired edge gage of a plate and the predicted stretch of the mill at the plate edges at the expected force levels;

(b) establishing an offset in accordance with the un- 6 loaded configuration of the rolls and the width of the plate to be rolled, said offset being substantially equal to the total space existing between adjacent roll surfaces in an unloaded condition at a location correponding to the edge of the plate to be rolled;

(c) combining the base figure and the offset to establish the proper center line roll opening;

(d) positioning the rolls according to the proper center line roll opening; and

(e) passing the plate between the positioned rolls.

2. A gage control method as recited in claim 1 where in the offset is established as the product of the effective crown on the rolls and the square of the ratio of plate width to roll length.

3. A gage control method as recited in claim 1 wherein an approximate offset is established from the formula W-M k0 R where k is a constant determined by the unstressed configurations of the faces of the rolls, C is the effective crown of the rolls, W is the predetermined width of the plate, M is the minimum. plate width to be rolled at the mill stand, and R is the length of the mill rolls.

4. For use in a plate rolling mill wherein the roll positions are monitored by an indicator calibrated for the center line of the mill, a method of establishing the center line roll opening needed to roll a plate having a desired edge gage, said method including the steps of:

(a) establishing a base figure for the roll opening at the mill center line in accordance with the desired edge gage of a plate and the predicted stretch of the mill at the plate edges at the expected force levels;

(b) electrically computing an offset in accordance with the unloaded configuration of the rolls and the width of the plate to be rolled, said offset being substantially equal to the total space existing between adja cent roll surfaces in an unloaded condition at a location corresponding to the edge of the plate to be rolled;

(c) electrically summing the base figure and the offset to establish the proper center line roll opening; and

(d) passing the plate between rolls separated by the proper center line roll opening to reduce the gage of said plate.

5. A method as recited in claim 4 wherein the offset is electrically computed as the product of the effective crown on the rolls and the square of the ratio of plate width to roll length.

6. A method as recited in claim 4 wherein an approximate offset is electrically computed from the formula W-M k0 R M where k is a constant determined by the unstressed configurations of the faces of the rolls, C is the effective crown of the rolls, W is the predetermined width of the plate, M is the minimum plate width to be rolled at the mill stand, and R is the length of the mill rolls.

References Cited UNITED STATES PATENTS 3,253,438 5/1966 Stringer 72-12 3,387,470 6/ 1968 Smith, Jr. 728 3,330,142 7/1967 Thompson 72-8 3,365,920 1/1968 Maekawa et al. 7210 MILTON S. MEHR, Primary Examiner 

